STED Microscopy to Monitor Agglomeration of Silica Particles Inside A549 Cells

Abstract The widespread use of engineered nanomaterials increases the exposure of the materials to humans. Therefore, it is necessary to know how these materials interact with cells. One approach is to trace particles by fluorescent labeling. The aim of the present work was to study the behavior of silica particles in A549 cells. For the first time, we applied stimulated emission depletion (STED) microscopy for this approach. Therefore, SiO₂ particles conjugated with Atto647N were prepared by L‐arginine‐catalyzed hydrolysis of tetraethoxysilane. The Atto647N labeled SiO₂ particles exhibit a mean size of 128 ± 7 nm and a zeta‐potential of −11 mV in cell culture medium. STED microscopy enables subdiffraction resolution imaging of single Atto647N labeled SiO₂ particles not only in pure solution but also in a cellular environment. To visualize Atto647N labeled SiO₂ particles inside A549 cells, the membrane was labeled and image stacks, that give three‐dimensional information, were taken after 5, 24, and 48 h exposure of particles to cells. During this incubation period, an increase in particle uptake was observed and STED micrographs allowed us to evaluate the agglomeration of Atto647N labeled SiO₂ particles inside A549 cells. Our results show that STED microscopy is a powerful technique to study particles in a cellular environment.